Hard disk drives today must meet very stringent requirements. I current disk drive designs the read-write head flies only a few nanometers (nm) above the rotating disk surface, which the read-write head accesses. Contact between the read-write head and the disk surface tends to disrupt data access and possibly damage the data stored on the disk surface. Further, it is difficult to determine when the read-write head contacts the disk surface. Without knowing when there is contact, it is difficult, and often impossible, to avoid and/or fix such contacts.
What is needed are methods and apparatus which can detect read-write head contact with the accessed disk surface. What is further needed are methods of avoiding such contacts during the normal operation of the hard disk drive.
Today, many hard disk drive manufacturers use a form of predictive failure analysis known as SMART (Self-Monitoring Analysis and Reporting Technology) to monitor hard disk drive performance parameters to estimate predictable failures of the hard disk drive. Hard disk drive failures are classified as predictable failures, or unpredictable failures. Unpredictable failures occur without warning and often involve failures in integrated circuits and conductors. Predictable failures usually involve the observable changes in a performance parameter.
These performance parameters often include estimates of the following. A decline in the flying height of a read-write head over the accessed disk surface may indicate a coming head crash. If the hard disk drive is remapping many sectors due to internally detected errors, it is probably beginning to fail. When the Error Control and Correction (ECC) usage increases, whether or not the errors are correctable, this may signal the beginning of disk failure. Changes in spin-up time may indicate problems with the spindle motor. Increased internal temperature may indicate problems with the spindle motor. Reductions in data transfer rate can indicate any of several problems. These problems may lead to the failure of the hard disk drive. What is needed is increased sensitivity to the hard disk drive to improve the ability to predict hard disk drive failures.
Hard disk drives implement one of two approaches to parking the voice coil actuators in the hard disk drive. One approach uses a special latch mechanism located outside the disk(s), often known as an Impact Rebound crash stop. The other approach parks the sliders containing the read-write head(s) near the spindle shaft, which is known as the Crash Start-Stop approach. The Crash Start-Stop mechanism puts the read-write heads into contact with the disk surfaces near the spindle to park the voice coil actuator.
Additionally, a hard disk drive is a sealed unit. During the manufacturing process, once the hard disk drive is sealed, the ability to detect contact between the read-write head and the accessed disk surface is often impossible. In hard disk drives employing the Crash Start-Stop mechanism, the details of when the contact occurs is often important to determine the reliability of the unit, particularly regarding parking the voice coil actuator and unparking, or spinning up, the hard disk drive for normal operations.
To summarize, methods and apparatus are needed which can detect read-write head contact with their accessed disk surface. Further, methods are needed which avoid such contacts during the normal operation of the hard disk drive. Extensions to the Self-Monitoring Analysis and Reporting Technology are needed which include the apparatus and methods necessary to detect contact(s) and create a contact event log. Further extensions are needed which can predict problems based upon the contact event log. Manufacturing processes are needed which can detect contacts after a hard disk drive is sealed and use that information to improve reliability estimates for the hard disk drive during the burn-in of the sealed hard disk drive.